1. Field of the Invention
The present invention relates to a method for controlling the starting of an internal combustion engine comprising an exhaust aftertreatment device that requires a minimal threshold temperature for proper operation. Moreover, the invention relates to a system comprising an internal combustion engine, an exhaust gas aftertreatment device, an electrical generator, and an engine controller.
2. Background and Summary of the Invention
During the last few years, regulations for the protection of the environment have become increasingly stringent. This makes it more and more difficult to meet legal requirements, though exhaust aftertreatment devices like three-way catalysts, conventional oxidation catalysts, and particulate filters are standard today.
According to a first aspect of the invention, a method for controlling the starting of an internal combustion engine is provided. The engine is coupled to an exhaust aftertreatment device that has a minimal threshold temperature for proper operation. During a certain period of time after engine start, the following steps are performed: a) increasing the electrical load of an electrical generator that is driven by the engine; and b) throttling the air intake to reduce the intake manifold pressure to a target pressure.
During warm-up of the engine, the aftertreatment device is possibly cold and, therefore, not at its optimal working range or possibly not operative at all. Exhaust gases are therefore released into the atmosphere essentially untreated. This leads to high emissions during engine start, which represent a considerable fraction of the total emissions of the internal combustion engine. An advantage of the present method is a considerable reduction in emissions of the internal combustion engine by focusing on the starting period of the engine.
The method according to the present invention causes additional power to be consumed by the loads that are coupled to the generator. This leads to a higher load for the engine which, in turn, results in faster warm-up of the exhaust gases. Thus, the period of time during which the aftertreatment device is not operative is reduced. Throttling contributes further to this effect because throttling air flow through the engine means that less mass has to be heated with a given amount of energy, yielding higher combustion temperatures in the cylinders. Furthermore, efficiency of the engine is reduced, partially due to an increase in pumping losses. A higher fuelling rate is used to provide the desired torque, thus leading to a higher temperature of the exhaust gases.
The electrical loads that are coupled to the generator preferably comprise electrical consumers that are present in a vehicle anyway, e.g., at least one glow plug of the engine or an electrical heater of the cabin or the windshield. The advantage of said consumers is that their short-term operation as additional load will not be noticed by the driver.
According to another aspect of the invention, exhaust gas recirculation is reduced or stopped during throttling. Due to the reduction of the intake manifold pressure, the pressure difference between intake manifold and exhaust manifold increases, which may lead to an excessive amount of exhaust gas recirculation. This excessive exhaust gas recirculation is prevented by reducing or stopping exhaust gas recirculation, i.e., by closing the exhaust gas recirculation valves.
If a turbine with variable geometry is present in the engine, it may be operated open-loop only during throttling. This prevents turbocharger over-speed which might result from throttling the intake while attempting to stabilize intake manifold pressure.
Preferably, the desired exhaust temperature is attempted by increasing electrical load on the generator alone. If this does not succeed, however, throttling is also carried out. The decision to include throttling is preferably based on the exhaust temperature downstream of the aftertreatment device. Thus, throttling is carried out if the exhaust gas temperature downstream of the aftertreatment device is below a given threshold temperature.
The goal of the method, according to the present invention, is to reach a temperature of the exhaust gas that is above the threshold temperature for proper operation of the aftertreatment device as soon as possible after starting the engine. Consequently, increasing the electrical load and throttling are preferably stopped if the exhaust gas temperature has reached this threshold, thus limiting the time spent within the exceptional engine mode of steps a) and b).
To avoid undesirable implications of increasing electrical load on the generator and throttling, they are preferably carried out only when the temperature of the engine at start is within a certain temperature interval, i.e., not too high and not too low.
Preferably, the combustion engine is a diesel engine and the aftertreatment device comprises an oxidation catalyst. Presently, diesel engines emit most of their cycle emissions of CO and HC during engine and catalyst warm-up. The oxidation catalyst does not convert the CO and HC leaving the engine until it has reached a temperature of about 200xc2x0 C. Therefore, the advantages of the present invention are most prominent in conjunction with such a diesel engine and an oxidation catalyst. Here, a considerable reduction in total emissions can be achieved.
The above advantages and other advantages, objects, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.